A vehicle body floor portion structure in which a locker, a floor panel, a dash panel, across member, a front cross member and a rear cross member are made of carbon fiber reinforced plastic is conventionally known (for example, refer to Japanese Patent Application Publication No. 2008-155700 (JP 2008-155700 A), Japanese Patent Application Publication No. 1-132474 (JP 1-132474 A) and Japanese Patent Application Publication No. 6-64559 (JP 6-64559 A). Also, a floor portion structure that improves a load transmission efficiency at a time of a collision although the floor portion structure is not made of the resin is conventionally known (for example, refer to Japanese Patent Application Publication No. 2003-285766 (JP 2003-285766 A), Japanese Patent Application Publication No. 2008-49894 (JP 2008-49894 A) and Japanese Utility Model Application Publication No. 3-84286 (JP 3-84286 U).